Lesson 1.2.3

1.2.3 page 3

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The Adrenal Medulla

 

fight or flight responses; short term stress responses that ensure increased amounts of glucose and oxygen available to muscle cells for cellular respiration, which results in increased available energy for use by muscles

 

epinephrine: a hormone produced by the adrenal medulla in response to stress; also called adrenaline; the adrenal gland produces about 80% epinephrine and 20% norepinephrine

 

norepinephrine; a second hormone produced by the adrenal medulla in response to stress but in much smaller quantities; about 20% of adrenal medulla secretions are norepinephrine

In Module 1, you studied sympathetic nerve activity, which is collectively called the “fight or flight” responses. These responses prepare the body for immediate action. To refresh your memory and summarize what these responses are, read the following two pages of your text: page 397 and page 452.

 

Nerve impulses from the sympathetic nerve system stimulate the adrenal medulla to release epinephrine and norepinephrine. These hormones circulate in the bloodstream and enhance the activities of the sympathetic nervous system. Together the sympathetic nervous system and the release of hormones from the adrenal medulla provide the resources (oxygen and blood glucose) for energy release by aerobic cellular respiration and allow the body to perform far beyond its capacity. You may have heard stories of how a mother fearlessly fought off a bear which was mauling her child, or a man lifting a car to free an accident victim pinned beneath it. These incredible feats were performed because the sympathetic nervous system stimulated the adrenal medulla to release a burst of adrenaline which enabled a lot of energy to be released by metabolism.

 

© John Bell/shutterstock

 

Watch and Listen

 

The following videos will reinforce your understanding of how the adrenal medulla works to combat the effects of what is sometimes called short term stress.

 

Epinephrine Release

 

Body’s Responses Norepinephrine

 

Symptoms of Stress

 

Try This

 

TR 1.

 

To review the concepts on the short term stress response, complete the following questions. After checking your answers, file them in your course folder.

  1. Describe a “fight” and a “flight” response and include the biological mechanism behind these responses.

  2. Identify three groups of stress stimuli (categories of things that cause stress).

  3. Explain how the hypothalamus is involved in the release of epinephrine and norepinephrine by the adrenal medulla. You may choose to use a flow chart to illustrate your response.

Check your work.
Self-Check Answers

 

TR 1.

  1. The short-term responses to stress are commonly referred to as the “fight or flight” responses. Like the nerve impulses of the sympathetic nervous system, the hormones of the adrenal medulla prepare the body by increasing the levels of oxygen and glucose and their distribution to the muscles and tissues. To increase the level of oxygen in the blood breathing rate increases and bronchioles dilate go get more oxygen into the lungs for diffusion. To increase the level of glucose in the blood, the liver and muscles are stimulated to convert stored glycogen into glucose. Heart rate, cardiac output, and blood pressure increase so that distribution of the blood to the tissues is greater and faster. Peripheral or skin blood vessels, as well as those to the digestive system, constrict and redirect blood to the muscles and tissues that need more blood. Cellular respiration is increased and releases more energy to deal with the situation or to quickly run away. In addition, sweating increases to deal with the extra heat produced from increased metabolism (cellular respiration), pupils dilate so more light enters the eyeball and increases visual acuity so that the danger can be seen more clearly.

  1. Three groups of stress stimuli may be infection, injury to the body, or emotional stimuli such as fear, anger, or extreme sadness.

  1. The adrenal medulla is composed of modified neurons. Neurons from the sympathetic nervous system of the ANS, whose centres are located in the hypothalamus, directly stimulate the cells of the adrenal medulla to produce epinephrine and norepinephrine. OR A flow chart may resemble the following: